1. Field of the Art
This invention relates to a resin which contains 5-membered rings and double bonds in the main polymer chain thereof, is very reactive and also has excellent properties of heat resistance, stiffness and high impact resistance.
Currently in petrochemical industries, the naphtha of petroleum fractions is thermally cracked or decomposed to produce olefins such as ethylene and propylene. These olefins are used as the starting materials for a variety of chemicals such as ethylene oxide and acrylic acid or for a variety of synthetic resins such as polyethylene and polypropylene.
The C.sub.5 fractions having 5 carbon atoms obtained as by-products in the thermal cracking of naphtha have hardly been utilized. Of these C.sub.5 fractions, only isoprene is industrially used as material for production of synthetic rubbers, and most of the fractions are consumed as fuels.
2. Prior Art
Of these C.sub.5 fractions, cyclopentadiene is obtained in the largest amount. Cyclopentadiene is so reactive that the conversion of cyclopentadiene to a novel high-value products such as cyclopentene and norbornene derivatives is expected.
Especially interesting as novel engineering plastics is a polymer obtained by subjecting a norbornene derivative monomer to ring-opening polymerization in the presence of a metathesis catalyst such as tungsten or molybdenum. More specifically, a ring-opened polymer of 5-norbornene-2-carboxylic acid, if it can be obtained by subjecting cyclopentadiene and acrylic acid to the Diels-Alder reaction, is expected to provide an engineering plastic having high heat resistance because of its carboxylic acid groups. The ring-opening polymerization, however, does not take place because of the strong polarity of the carboxylic acid groups. Thus, in the present condition, it is industrially impossible to subject 5-norbornene-2-carboxylic acid to ring-opening polymerization directly.
On the other hand, a process for subjecting such ester compounds as methyl 5-norbornene-2-carboxylate or ethyl 5-norbornene-2-carboxylate to ring-opening polymerization in the presence of a metathesis catalyst has been disclosed by Japanese Patent Laid-Open No. 77999/1974. The ring-opened polymer which consists of the ester compound alone, is inferior in heat resistance and high impact property, has limited uses, and lacks industrial values for resin materials.
The present inventors have once proposed a process for preparation of the ring-opened polymer of 5-norbornene-2-carboxylic acid which comprises dissolving a ring-opened polymer of the above-mentioned ester compound in an organic solvent selected from ketones, tetrahydrofuran, dioxane, dimethylformamide and dimethylsulfoxide, and then reacting the resulting solution by addition thereto of an aqueous alkali solution, and further neutralizing the reaction product by addition thereto of an acid. The resulting polymer having a trans-form content of less than 40%, however, exhibits low heat resistance and also has a little value for industrial uses. The copolymer having a low transform content and consisting of the structural units (A) and (B) not only has low heat resistance but also is inferior in stiffness and high impact property. The uses thereof are also limited.
The ring-opened polymer consisting of 5-norbornene-2-carboxylic acid, even when it has a trans-form content of 40% or more, is not satisfactory with respect to a high impact property, although it has excellent heat resistance. Thus, a notatable feature could not be found especially in the polymer in comparison with other competitive resins.
The present inventors have made intensive researches on the production of such resins, and accomplished the present invention.